1. Field of the Invention
The present invention relates to a cam mechanism for preventing the inclination and fluctuation (e.g. accidental movement) of a lens barrel with respect to an optical axis, which would otherwise occur during zooming, in a camera, particularly in a lens shutter type of camera having a zoom lens.
2. Description of Related Arts
The assignee of the present application has proposed a back focus adjusting mechanism of a zoom lens camera in which a distance between a plane of a rearmost lens of the zoom lens and a film plane can be easily adjusted, as disclosed for example in Japanese Patent Application No. 63-32544, Japanese Utility Model Application Nos. 63-18457 and 63-18458, and U.S. Patent applicaton Ser. No. 310,191.
In a zoom lens, as disclosed in these prior applications, front and rear groups of lenses are supported by a frame (lens barrel) of the front lens group which can be moved in the optical axis direction in accordance with the rotation of a cam ring. The cam ring is provided with four cam grooves, two for the front lens group and two for the rear lens group. Pins which are provided on the frames of the front lens group and rear lens group are fitted in the respective cam grooves.
In the lens supporting mechanism having the cam construction mentioned above, if the travel distance of the front lens group frame is large, the length of the engagement between the front lens group frame and the cam ring at the forward end of the movement of the front lens group frame is insufficient, so that the front lens group frame tends to be inclined or accidentally moved with respect to the optical axis, resulting in a deviated optical axis.